Catalysts are used in large acid or fertilizer plant vessels to remove products or impurities during the manufacturing process. At a certain point in the life of the catalyst, the catalyst granules have attracted all the materials they can and must be cleaned of these material. In order to clean materials from a catalyst, a process known as screening is required. Screening is the mechanical shaking or vibrating of the catalyst granules to remove the material which may be in the form of dust or chips. After screening, the dust and chips go to disposal and the cleaned regenerated catalyst is returned to the vessel to be reused.
The vessels in which such catalysts are used such as those used in acid plant vessels are relatively large vertically oriented vessels having a diameter of 15 feet or more. The catalyst may be arranged in horizontal layers and a vessel may have several beds and there may be several different layers within the catalyst beds. In order to conduct the screening process, the catalyst is manually removed from the bed within the vessel and remotely screened. The screened catalyst is then replaced within the vessel. These vessels are operated at relatively high temperature, sufficiently hot that an unprotected person cannot enter the vessel immediately following shut down. As the vessels are operated at high temperature, normally, work crews cannot enter the vessel until the vessel has cooled.
In many cases, the vessels have relatively restricted access to the area of the vessel between adjacent beds. Often the access hatch or opening to a vessel may be of the order of 2 to 3 feet square. In unusual cases, the access opening may be as large as 4 feet by 3 feet. The size of such openings will permit a person to pass through the opening but makes it inconvenient to use any type of existing powered equipment within the vessel.
When the vessel is operated at high temperature, the vessel must be allowed to cool to a temperature at which human beings may enter the vessel. If the human beings are protected by a fully enclosing protective suit which is provided with cooling means, the persons may enter the vessel at warmer temperatures. However, once in the vessel, the worker must commence the job of removing the catalyst using hand held tools. This is difficult while wearing such a protective suit and maneuvering through restricted spaces.
In other cases, the vessel is operated at cooler temperatures. However, even when cooler temperatures are used in the process, the restrictions on access remain and the vessel is none-the-less full of gases which are hazardous to health. Thus, even with a vessel operating a cooler process, a person entering the vessel must be in a protective suit and provided with a breathing air supply to protect against the hazardous conditions found within the vessel.
Accordingly, it would be advantageous, if equipment were to be developed which can gain entry into a vessel and work within such a vessel on a catalyst bed to remove the catalyst from the reactor vessel while not damaging the catalyst during removal.